1. Field of the Invention
This invention relates generally to the hot-forming of metal and more particularly, to apparatus for producing a hot-formed product from a cast metal without homogenizing the cast metal prior to hot-forming.
2. Description of the Prior Art
In the hot-forming of a cast metal to produce a hot-formed product, cracking and splitting of the cast metal is frequently encountered as the result of a characteristic commonly known as hot shortness. Moreover, cast metal usually has internal stresses due to non-uniform cooling rates during casting or due to straightening the cast metal after casting. These stresses also cause cracking and splitting of the cast metal during hot-forming.
The cracking and splitting of a cast metal as the result of hot shortness or internal stresses can be avoided by homogenizing the cast metal prior to hot-forming. This is because homogenizing a cast metal disperses alloying and other elements and compounds from grain boundaries between dendrites within the cast metal into the dendrites. The result is an increase in tensile strength to a degree sufficient to resist cracking and splitting because of hot shortness or internal stresses.
The homogenizing of a cast metal requires that the cast metal be held at a temperature above the recrystallization temperature of the cast metal for an extended period of time. When the cast metal to be hot-formed is initially at room temperature, the elevated temperature and the period of time at this elevated temperature required for homogenizing the cast metal are obtained simply by reheating the cast metal to hot-forming temperature since this provides time and temperature conditions sufficient for homogenization. When the cast metal to be hot-formed has not been allowed to cool to room temperature from its casting temperature, the elevated temperature and the period of time at this elevated temperature required for homogenization of the cast metal can be obtained only by holding the cast metal at approximately casting temperature for an extended period of time. This is commonly known as soaking. Thus, whether a cast metal to be hot-formed is at room temperature or at casting temperature prior to hot-forming, homogenization of the cast metal prior to hot-forming is time consuming and frequently requires extensive equipment and space.
Moreover, neither of the above techniques for homogenizing a cast metal is suited to the continuous casting and hot-forming of a cast metal since it is impractical to cool and reheat a cast metal as it is being continuously cast and hot-formed so as to provide for homogenizing of the cast metal before it is fed to the hot-forming means and since it is impractical to hold a cast metal as it is being continuously cast at an elevated temperature for the length of time required to accomplish homogenization of the cast metal while it is being continuously fed from a casting means to a hot-forming means. Thus, the homogenization of a cast metal prior to hot-forming is a generally unsatisfactory method of preventing splitting and cracking of the cast metal during hot-forming and is a particularly unsatisfactory method of accomplishing this objective where it is desired to continuously hot form a continuously cast metal.